Most spring assemblies are constructed by attaching wires longitudinally and transversely to a border wire and then attaching the coils to the wires with their axes perpendicular to the plane of the wires. The coils are attached by twisting portions of the end loops of the coils about the wires, or by twisting portions of the wires about the end loops, or by using separate clamps to attach the end loops to the wires and/or by using locking wires. In all such structures the attachment requires the use of special tools and is a manual operation which requires considerable time, is tedious, difficult and must be preformed at the place of manufacture. Recently Applicant developed a snap-on spring assembly which is the subject matter of U.S. Pat. No. which eliminated for the most part the foregoing problems. This was achieved by providing deviations in the end loops of the coils and also in the wires which could be interengaged by deformation and become locked to each other by allowing the parts to return to their initial configuration. In the patent the wires were provided with downwardly depressed portions and the end loops of the coils with inwardly bent portions, the end loops were placed against the undersides of the wires and the inwardly bent portions spread apart to clear the wires and then allowed to retract inwardly thru the downwardly depressed portions of the wires. This was the first structure of the kind wherein the composite parts could be shipped from the place of manufacture to the customer unassembled and assembled by the customer without need for special tools and/or skilled assistance. A variation of this was patented by Reupel U.S. Pat. No. 3,766,578 wherein deviations in the form of hooks were made in the opposed wires at the seats and the end loops of the coils were deformed sufficiently to clear the hooks so as to allow the hooks to be entered into the open ends of the coils whereupon the end loops were released and became locked to the wires. This constituted a second way of providing for a snap-on assembly of the coils to the grid. In each instance the construction constituted an advance in the art and enabled manufacture and shipping of the parts to the customer for assembly thus making tremendous savings in shipping and assembly costs. This invention is a further improvement in that it provides for a snap-on structure which is more stable in that when attached, rocking and twisting of the coils relative to the wires will be substantially eliminated. This is done by increasing the interlocking surfaces and the angular disposition of the parts so as to resist relative movement.